System and method for positioning teeth

ABSTRACT

Methods and apparatus fit a set of upper and lower teeth in a masticatory system by generating a computer representation of the masticatory system and computing an occlusion based on interactions in the computer representation of the masticatory system.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.10/133,155 (Attorney Docket No. 18563-004910/AT-00106.1), filed Apr. 26,2002, and was a continuation of U.S. application Ser. No. 09/169,036(Attorney Docket No. 18563-004900/AT00106), filed Oct. 8, 1998, the fulldisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is related generally to the field oforthodontics, and more particularly to a system and a method forgradually repositioning teeth.

[0003] A fundamental objective in orthodontics is to realign a patient'steeth to positions where the teeth function optimally and aesthetically.Typically, appliances such as braces are applied to the teeth of thepatient by a treating orthodontist. Each appliance exerts continualforces on the teeth which gradually urge the teeth toward their idealpositions. Over a period of time, the orthodontist adjusts theappliances to move the teeth toward their final destination.

[0004] The process of attaching the braces to teeth is tedious andpainful. Additionally, each visit to the orthodontist is time consumingand expensive. The process is further complicated by uncertainties indetermining a final arrangement for each tooth. Generally, the finaltooth arrangement is determined by the treating orthodontist who writesa prescription. Traditionally, the prescription is based on theorthodontist's knowledge and expertise in selecting the intended finalposition of each tooth and without a precise calculation of forces beingexerted on the teeth when they contact each other.

BRIEF SUMMARY OF THE INVENTION

[0005] The invention provides a method for fitting a set of upper andlower teeth in a masticatory system of a patient. The method generates acomputer representation of the masticatory system of the patient; anddetermines an occlusion from the computer representation of themasticatory system.

[0006] Implementations of the invention include one or more of thefollowing. The occlusion may be a static occlusion, which is determinedby modeling an ideal set of teeth; automatically applying the ideal setof teeth to the computer representation of the masticatory system of thepatient; and optimizing the position of the patient's teeth to fit theideal set of teeth. The modeling step may select one or more arch formsspecifying the ideal set of teeth. The applying step may includeregistering a model of the upper and lower teeth with a model of themasticatory system; simulating the motion of the jaws to generatecontact data between the upper and lower teeth; and placing the tooth ina final position based on the contact data. The model may be registeredusing X-ray data, computed tomography data, or data associated with amechanical model. The simulating step may apply kinematics to the modelof the teeth or a constrained motion to the model of the tooth. Theplacing step may be based on a measure of undesirability to thecontacts. The position of the tooth may be determined according to themeasure of undesirability, such as by minimizing the measure ofundesirability. The measure of undesirability may be a function of oneor more of Peer Assessment Rating (PAR) metrics, distance-based metricsand shape-based metrics. The simulating step may provide a library ofmotions with protrusive motions, lateral motions, or tooth-guidedmotions. Physical forces may be applied to the patient's jaws. Thecomputer representation of the masticatory system may be updated withnew patient data. The new patient data may be used with the old data inapplying a final position transform to the second teeth model. Thematching step may compare correspondences between the first and secondteeth models. The correspondences include feature correspondences. Thefinal position transform may include information from a newprescription.

[0007] Other implementations include one or more of the following. Theocclusion determining step includes determining one or more indicesbased on the tooth position; determining an optimality index from theindices; and setting the tooth according to the optimality index. Theoptimality determining step includes minimizing the optimality index.The indices may be based on a Peer Assessment Rating (PAR) index, adistance metric, or a shape metric. The shape metric may be derived froman arch. The indices may be based on an occlusional index or anorthodontic index. The setting of the teeth may be based on acorrespondence of tooth features, including a correspondence of toothcusps, tooth fossae, or tooth ridges. The optimality index may beoptimized using one of simulated annealing technique, hill climbingtechnique, best-first technique and heuristics technique. Theimplementation may determine whether a tooth movement reduces the index.The tooth movement may be made along each major axis and may includerotations. The tooth position may be updated if the tooth movementreduces the index.

[0008] In a second aspect, a computer-implemented apparatus defines afit between a set of upper and lower teeth in a masticatory system of apatient. The apparatus comprises instructions operable to cause aprogrammable processor to generate a computer representation of themasticatory system of the patient; and determining an occlusion from thecomputer representation of the masticatory system.

[0009] Implementations of this aspect include one or more of thefollowing. The invention may determine a static occlusion throughinstructions to model an ideal set of teeth; automatically apply theideal set of teeth to the computer representation of the masticatorysystem of the patient; and optimize the position of the patient's teethto fit the ideal set of teeth. The occlusion determining instruction mayalso include instructions to: determine one or more indices based on thetooth position; determine an optimality index from the indices; and setthe tooth according to the optimality index.

[0010] In another aspect, a system for defining a fit between a set ofupper and lower teeth in a masticatory system of a patient includes aprocessor; a display device coupled to the processor; and a data storagedevice coupled to the processor, the data storage device storinginstructions operable to cause the processor to generate a computerrepresentation of the masticatory system of the patient and determine anocclusion from the computer representation of the masticatory system.

[0011] In another aspect, a system for generating one or more appliancesfor a patient includes a processor; a display device coupled to theprocessor; a data storage device coupled to the processor; a scannercoupled to the processor for providing data to model the masticatorysystem; means for defining a fit between a set of upper and lower teethin a masticatory system of the patient; and a dental appliancefabrication machine coupled to the processor for generating theappliances in accordance with the fit of the teeth.

[0012] Advantages of the invention include one or more of the following.When a prescription or other final designation is provided, a computermodel can be generated and manipulated to match the prescription. Theprescription may be automatically interpreted in order to generate animage as well as a digital data set representing the final tootharrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an elevational diagram showing the anatomicalrelationship of the jaws of a patient.

[0014]FIG. 2A illustrates in more detail the patient's lower jaw andprovides a general indication of how teeth may be moved by the methodsand apparatus of the present invention.

[0015]FIG. 2B illustrates a single tooth from FIG. 2A and defines howtooth movement distances are determined.

[0016]FIG. 2C illustrates the jaw of FIG. 2A together with anincremental position adjustment appliance which has been configuredaccording to the methods and apparatus of the present invention.

[0017]FIG. 3 is a block diagram illustrating a process for producingincremental position adjustment appliances.

[0018]FIG. 4 is a flow chart illustrating a process for optimizing afinal placement of the patient's teeth.

[0019]FIG. 5 is a flow chart illustrating a process for performingfunctional occlusion on the patient's teeth.

[0020]FIG. 6 is a flow chart illustrating an optional process forincorporating midtreatment information to the final placement of thepatient's teeth.

[0021]FIG. 7 is a block diagram illustrating a system for generatingappliances in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022]FIG. 1 shows a skull 10 with an upper jaw bone 22 and a lower jawbone 20. The lower jaw bone 20 hinges at a joint 30 to the skull 10. Thejoint 30 is called a temporomandibular joint (TMJ). The upper jaw bone22 is associated with an upper jaw 101, while the lower jaw bone 20 isassociated with a lower jaw 100.

[0023] A computer model of the jaws 100 and 101 is generated, and acomputer simulation models interactions among the teeth on the jaws 100and 101. The computer simulation allows the system to focus on motionsinvolving contacts between teeth mounted on the jaws. The computersimulation allows the system to render realistic jaw movements which arephysically correct when the jaws 100 and 101 contact each other. Themodel of the jaw places the individual teeth in a treated position.Further, the model can be used to simulate jaw movements includingprotrusive motions, lateral motions, and “tooth guided” motions wherethe path of the lower jaw 100 is guided by teeth contacts rather than byanatomical limits of the jaws 100 and 101. Motions are applied to onejaw, but may also be applied to both jaws. Based on the occlusiondetermination, the final position of the teeth can be ascertained.

[0024] Referring now to FIG. 2A, the lower jaw 100 includes a pluralityof teeth 102, for example. At least some of these teeth may be movedfrom an initial tooth arrangement to a final tooth arrangement. As aframe of reference describing how a tooth may be moved, an arbitrarycenterline (CL) may be drawn through the tooth 102. With reference tothis centerline (CL), each tooth may be moved in orthogonal directionsrepresented by axes 104, 106, and 108 (where 104 is the centerline). Thecenterline may be rotated about the axis 108 (root angulation) and theaxis 104 (torque) as indicated by arrows 110 and 112, respectively.Additionally, the tooth may be rotated about the centerline, asrepresented by an arrow 114. Thus, all possible free-form motions of thetooth can be performed.

[0025]FIG. 2B shows how the magnitude of any tooth movement may bedefined in terms of a maximum linear translation of any point P on atooth 102. Each point P1 will undergo a cumulative translation as thattooth is moved in any of the orthogonal or rotational directions definedin FIG. 2A. That is, while the point will usually follow a nonlinearpath, there is a linear distance between any point in the tooth whendetermined at any two times during the treatment. Thus, an arbitrarypoint P1 may in fact undergo a true side-to-side translation asindicated by arrow d1, while a second arbitration point P2 may travelalong an arcuate path, resulting in a final translation d2. Many aspectsof the present invention are defined in terms of the maximum permissiblemovement of a point P1 induced on any particular tooth. Such maximumtooth movement, in turn, is defined as the maximum linear translation ofthat point P1 on the tooth which undergoes the maximum movement for thattooth in any treatment step.

[0026]FIG. 2C shows one adjustment appliance 111 which is worn by thepatient in order to achieve an incremental repositioning of individualteeth in the jaw as described generally above. The appliance is apolymeric shell having a teeth receiving cavity. This is described inU.S. application Ser. No. 09/169,276, filed Oct. 8, 1998, which claimspriority from U.S. Pat. No. 5,975,893, which in turn claims priorityfrom provisional application No. 06/050,352, filed Jun. 20, 1997(collectively the “prior applications”), the full disclosures of whichare incorporated by reference.

[0027] As set forth in the prior applications, each polymeric shell maybe configured so that its tooth receiving cavity has a geometrycorresponding to an intermediate or final tooth arrangement intended forthe appliance. The patient's teeth are repositioned from their initialtooth arrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances are generated at the beginning of the treatment,and the patient wears each appliance until the pressure of eachappliance on the teeth can no longer be felt. At that point, the patientreplaces the current adjustment appliance with the next adjustmentappliance in the series until no more appliance remains. Conveniently,the appliances are generally not affixed to the teeth and the patientmay place and replace the appliances at any time during the procedure.The final appliance or several appliances in the series may have ageometry or geometries selected to overcorrect the tooth arrangement,i.e., have a geometry which would (if fully achieved) move individualteeth beyond the tooth arrangement which has been selected as the“final.” Such overcorrection may be desirable in order to offsetpotential relapse after the repositioning method has been terminated,i.e., to permit some movement of individual teeth back toward theirprecorrected positions. Overcorrection may also be beneficial to speedthe rate of correction, i.e., by having an appliance with a geometrythat is positioned beyond a desired intermediate or final position, theindividual teeth will be shifted toward the position at a greater rate.In such cases, the use of an appliance can be terminated before theteeth reach the positions defined by the appliance.

[0028] The polymeric shell 111 can fit over all teeth present in theupper or lower jaw. Often, only certain one(s) of the teeth will berepositioned while others of the teeth will provide a base or an anchorregion for holding the appliance 111 in place as the appliance 111applies a resilient repositioning force against the tooth or teeth to berepositioned. In complex cases, however, multiple teeth may berepositioned at some point during the treatment. In such cases, theteeth which are moved can also serve as a base or anchor region forholding the repositioning appliance.

[0029] The polymeric appliance 111 of FIG. 2C may be formed from a thinsheet of a suitable elastomeric polymer, such as Tru-Tain 0.03 in,thermal forming dental material, available from Tru-Tain Plastics,Rochester, Minnesota. Usually, no wires or other means will be providedfor holding the appliance in place over the teeth. In some cases,however, it will be desirable or necessary to provide individual anchorson teeth with corresponding receptacles or apertures in the appliance100 so that the appliance can apply an upward force on the tooth whichwould not be possible in the absence of such an anchor.

[0030]FIG. 3 shows a process 200 for producing the incremental positionadjustment appliances for subsequent use by a patient to reposition thepatient's teeth. As a first step, an initial digital data set (IDDS)representing an initial tooth arrangement is obtained (step 202). TheIDDS may be obtained in a variety of ways. For example, the patient'steeth may be scanned or imaged using X-rays, three dimensional X-rays,computer-aided tomographic images or data sets, or magnetic resonanceimages, among others. The teeth data may be generated by a destructivescanner, as described in the incorporated-by-reference U.S. applicationSer. No. 09/169,276, filed Oct. 8, 1998.

[0031] The IDDS is then manipulated using a computer having a suitablegraphical user interface (GUI) and software appropriate for viewing andmodifying the images. More specific aspects of this process will bedescribed in detail below.

[0032] Individual tooth and other components may be segmented orisolated in the model to permit their individual repositioning orremoval from the digital model. After segmenting or isolating thecomponents, the user will often reposition the tooth in the model byfollowing a prescription or other written specification provided by thetreating professional. Alternatively, the user may reposition one ormore teeth based on a visual appearance or based on rules and algorithmsprogrammed into the computer. Once the user is satisfied, the finalteeth arrangement is incorporated into a final digital data set (IDDS)(step 204). The IDDS is used to generate appliances that move the teethin a specified sequence. First, the centers of each tooth model may bealigned using a number of methods. One method is a standard arch. Then,the teeth models are rotated until their roots are in the propervertical position. Next, the teeth models are rotated around theirvertical axis into the proper orientation. The teeth models are thenobserved from the side, and translated vertically into their propervertical position. Finally, the two arches are placed together, and theteeth models moved slightly to ensure that the upper and lower archesproperly mesh together. The meshing of the upper and lower archestogether is visualized using a collision detection process to highlightthe contacting points of the teeth.

[0033] Based on both the IDDS and the FDDS, a plurality of intermediatedigital data sets (INTDDSs) are defined to correspond to incrementallyadjusted appliances (step 206). Finally, a set of incremental positionadjustment appliances are produced based on the INTDDs and the FDDS(step 208).

[0034] In step 204, final positions for the upper and lower teeth in amasticatory system of a patient are determined by generating a computerrepresentation of the masticatory system. An occlusion of the upper andlower teeth is computed from the computer representation; and afunctional occlusion is computed based on interactions in the computerrepresentation of the masticatory system. The occlusion may bedetermined by generating a set of ideal models of the teeth. Each idealmodel in the set of ideal models is an abstract model of idealized teethplacement which is customized to the patient's teeth, as discussedbelow. After applying the ideal model to the computer representation,and the position of the teeth is optimized to fit the ideal model. Theideal model may be specified by one or more arch forms, or may bespecified using various features associated with the teeth.

[0035]FIG. 4 illustrates a process 300 which optimizes the finalplacement of the teeth based on teeth features. First, the process 300automatically or, with human assistance, identifies various featuresassociated with each tooth to arrive at a model of the teeth (step 302).An ideal model set of teeth is then generated either from casts of thepatient's teeth or from patients with a good occlusion (step 303).

[0036] From step 302, the process 300 positions the model of the teethin its approximate final position based on a correspondence of featuresto the ideal model (step 304). In that step, each tooth model is movedso that its features are aligned to the features of a correspondingtooth in the ideal model. The features may be based on cusps, fossae,ridges, distance-based metrics, or shape-based metrics. Shape-basedmetrics may be expressed as a function of the patient's arches, amongothers.

[0037] For example, cusp features associated with each tooth may beused. Cusps are pointed projections on the chewing surface of a tooth.In a detection stage, a possible cusp is viewed as an “island” on thesurface of the tooth, with the candidate cusp at the highest point onthe island. “Highest” is measured with respect to the coordinate systemof the model, but could just as easily be measured with respect to thelocal coordinate system of each tooth. The set of all possible cusps isdetermined by looking for all local maxima on the tooth model that arewithin a specified distance of the top of the bounding box of the model.First, the highest point on the model is designated as the firstcandidate cusp. A plane is passed through this point, perpendicular tothe direction along which the height of a point is measured. The planeis then lowered by a small predetermined distance along the Z axis.Next, all vertices connected to the tooth and which are above the planeand on some connected component are associated with the candidate cuspas cusps. This step is also referred to as a flood fill step. From eachcandidate cusp point, outward flooding is performed, marking each vertexon the model visited in this matter as part of the correspondingcandidate cusp. After the flood fill step is complete, every vertex onthe model is examined. Any vertex that is above the plane and has notbeen visited by one of the flood fills is added to the list of candidatecusps. These steps are repeated until the plane is traveled a specifieddistance.

[0038] After the detection stage, the cusp detection process may includea rejection stage where local geometries around each of cusp candidatesare analyzed to determine if they possess non-cusp-like features. Cuspcandidates that exhibit non-cusp-like features are removed from the listof cusp candidates. Various criteria may be used to identifynon-cusp-like features. According to one test, the local curvature ofthe surface around the cusp candidate is used to determine whether thecandidate possesses non-cusp-like features. Alternatively, a measure ofsmoothness is computed based on the average normal in an area around thecandidate cusp. If the average normal deviates from the normal at thecusp by more than a specified amount, the candidate cusp is rejected.

[0039] Next, the process 300 computes an orthodontic/occlusion index(step 306). One index which may be used is the PAR (Peer AssessmentRating) index. In addition to PAR, other metrics such as shape-basedmetrics or distance-based metrics may be used.

[0040] The PAR index identifies how far a tooth is from a goodocclusion. A score is assigned to various occlusal traits which make upa malocclusion. The individual scores are summed to obtain an overalltotal, representing the degree a case deviates from normal alignment andocclusion. Normal occlusion and alignment is defined as all anatomicalcontact points being adjacent, with a good intercuspal mesh betweenupper and lower buccal teeth, and with nonexcessive overjet andoverbite.

[0041] In PAR, a score of zero would indicate good alignment, and higherscores would indicate increased levels of irregularity. The overallscore is recorded on pre- and posttreatment dental casts. The differencebetween these scores represents the degree of improvement as a result oforthodontic intervention and active treatment. The eleven components ofthe PAR Index are: upper right segment; upper anterior segment; upperleft segment; lower right segment; lower anterior segment; lower leftsegment; right buccal occlusion; overjet; overbite; centerline; and leftbuccal occlusion. In addition to the PAR index, other indices may bebased on distances of the features on the tooth from their idealpositions or ideal shapes.

[0042] From step 306, the process 300 determines whether additionalindex-reducing movements are possible (step 308). Here, all possiblemovements are attempted, including small movements along each major axisas well as small movements with minor rotations. An index value iscomputed after each small movement and the movement with the best resultis selected. In this context, the best result is the result thatminimizes one or more metrics such as PAR-based metrics, shape-basedmetrics or distance-based metrics. The optimization may use a number oftechniques, including simulated annealing technique, hill climbingtechnique, best-first technique, Powell method, and heuristicstechnique, among others. Simulated annealing techniques may be usedwhere the index is temporarily increased so that another path in thesearch space with a lower minimum may be found. However, by startingwith the teeth in an almost ideal position, any decrease in the indexshould converge to the best result.

[0043] In step 308, if the index can be optimized by moving the tooth,incremental index-reducing movement inputs are added (step 310) and theprocess loops back to step 306 to continue computing theorthodontic/occlusion index. Alternatively, in the event that the indexcannot be optimized any more, the process 300 exits (step 312).

[0044] Turning now to FIG. 5, a process 320 for performing functionalocclusion is shown. Functional occlusion is a process for determininghow well the teeth fit together when the jaws move. The process 320first acquires tooth/arch jaw registration. This may be done usingconventional techniques such as X-ray, a computer tomography, or amechanical device such as a face bow transfer.

[0045] After acquiring the registration information, the process 320places digital dental models of the teeth in a digital articulationsimulator (step 324). The articulation simulator allows a subset of jawmovements such as bite-movements to be simulated, as described below.

[0046] From step 324, the process 320 simulates jaw motions (step 326).A simplified set of movement physics (kinematics) is applied to thedental models. The process 320 performs a simulation using a simplifiedset of interacting forces on the jaws 100 and 101 in relation to oneanother. The simplified physical simulation allows the system to focuson motions involving much contact between the jaws. The physicalsimulation allows the system to render realistic physically correct jawmovements when the jaws 100 and 101 come into contact with each other.

[0047] A range of simulated motion may be supplied using a library ofmotions. One typical motion supplied by the library is a protrusivemotion where the lower jaw 101 is moved forward and backward to bringthe front teeth on both jaws into contact with each other. Anothermotion is a lateral motion found in food chewing. The lateral motioninvolves moving the jaws 100 and 101 side to side. Other motions thatmay be supplied in the library include motions that are “tooth guided”0where the path of the lower jaw 100 is guided by the teeth in contactwith each other.

[0048] Next, the process 320 adjusts the final position based oncontacts observed during the simulation of motions in step 326 (step328). The result of the simulation is analyzed, the position of eachtooth can be adjusted if contacts associated with that tooth are deemedexcessive.

[0049] Finally, based on the contact data generated, the processdetermines whether additional motion simulations need to be done. Themotion simulation may be rerun until the contacts associated with eachtooth are acceptable to the treating orthodontist. The tooth modelmanipulation process can be done subjectively, i.e., the user may simplyreposition teeth in an aesthetically and/or therapeutically desiredmanner based on observations of the final position or based on thesimulation of contacts. Alternatively, rules and algorithms may be usedto assist the user in repositioning the teeth based on the contacts. Ifthe simulation needs to be repeated, the process loops back to step 326(step 330). Alternatively, the process exits (step 332).

[0050]FIG. 6 shows an optional process of 340 of incorporatingmidtreatment information to the final positioning process. First, adigital model incorporating dental information associated with thepatient is generated from a scan of the patient's teeth (step 342). Thescan may be performed using casts, X-rays or any of the conventionalscanning methods.

[0051] Next, the digital model is segmented into one model for eachtooth (step 344). Each tooth is then matched against a model associatedwith a prior scan developed at the beginning of the treatment plan (step346). The matching process is based on matching corresponding pointsbetween the current scan and the prior scan of the teeth. In most cases,the teeth segmented from the current scan retain the shapes determinedat the beginning of the treatment plan, and the matching process is easybecause the models should be similar to each other.

[0052] A final position transform is then applied to the new teeth model(step 348). The final position and specification from the prior model iscopied to the current model of the patient, and the final position isadjusted based on the new models, the new X-ray information or a newprescription (step 350). Step 350 basically involves rerunning theminimization process 300 (FIG. 4) described previously with the newinformation, which may be a slight change in the model, a change in theX-ray scan, or a change the prescription. Finally, the process 340 exits(step 352).

[0053]FIG. 7 is a simplified block diagram of a data processing system500. Data processing system 500 typically includes at least oneprocessor 502 which communicates with a number of peripheral devicesover bus subsystem 504. These peripheral devices typically include astorage subsystem 506 (memory subsystem 508 and file storage subsystem514), a set of user interface input and output devices 518, and aninterface to outside networks 516, including the public switchedtelephone network. This interface is shown schematically as “Modems andNetwork Interface” block 516, and is coupled to corresponding interfacedevices in other data processing systems over communication networkinterface 524. Data processing system 500 may include a terminal or alow-end personal computer or a high-end personal computer, workstationor mainframe.

[0054] The user interface input devices typically include a keyboard andmay further include a pointing device and a scanner. The pointing devicemay be an indirect pointing device such as a mouse, trackball, touchpad,or graphics tablet, or a direct pointing device such as a touchscreenincorporated into the display. Other types of user interface inputdevices, such as voice recognition systems, may be used.

[0055] User interface output devices may include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide nonvisualdisplay such as audio output.

[0056] Storage subsystem 506 maintains the basic programming and dataconstructs that provide the functionality of the present invention. Thesoftware modules discussed above are typically stored in storagesubsystem 506. Storage subsystem 506 typically comprises memorysubsystem 508 and file storage subsystem 514.

[0057] Memory subsystem 508 typically includes a number of memoriesincluding a main random access memory (RAM) 510 for storage ofinstructions and data during program execution and a read only memory(ROM) 512 in which fixed instructions are stored. In the case ofMacintosh-compatible personal computers the ROM would include portionsof the operating system; in the case of IBM-compatible personalcomputers, this would include the BIOS (basic input/output system).

[0058] File storage subsystem 514 provides persistent (nonvolatile)storage for program and data files, and typically includes at least onehard disk drive and at least one floppy disk drive (with associatedremovable media). There may also be other devices such as a CD-ROM driveand optical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

[0059] In this context, the term “bus subsystem” is used generically soas to include any mechanism for letting the various components andsubsystems communicate with each other as intended. With the exceptionof the input devices and the display, the other components need not beat the same physical location. Thus, for example, portions of the filestorage system could be connected over various local-area or wide-areanetwork media, including telephone lines. Similarly, the input devicesand display need not be at the same location as the processor, althoughit is anticipated that the present invention will most often beimplemented in the context of PCS and workstations.

[0060] Bus subsystem 504 is shown schematically as a single bus, but atypical system has a number of buses such as a local bus and one or moreexpansion buses (e.g., ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

[0061] Scanner 520 is responsible for scanning casts of the patient'steeth obtained either from the patient or from an orthodontist andproviding the scanned digital data set information to data processingsystem 500 for further processing. In a distributed environment, scanner520 may be located at a remote location and communicate scanned digitaldata set information to data processing system 500 over networkinterface 524.

[0062] Fabrication machine 522 fabricates dental appliances based onintermediate and final data set information received from dataprocessing system 500. In a distributed environment, fabrication machine522 may be located at a remote location and receive data set informationfrom data processing system 500 over network interface 524.

[0063] Various alternatives, modifications, and equivalents may be usedin lieu of the above components. Although the final position of theteeth may be determined using computer-aided techniques, a user may movethe teeth into their final positions by independently manipulating oneor more teeth while satisfying the constraints of the prescription.

[0064] Additionally, the techniques described here may be implemented inhardware or software, or a combination of the two. The techniques may beimplemented in computer programs executing on programmable computersthat each includes a processor, a storage medium readable by theprocessor (including volatile and nonvolatile memory and/or storageelements), and suitable input and output devices. Program code isapplied to data entered using an input device to perform the functionsdescribed and to generate output information. The output information isapplied to one or more output devices.

[0065] Each program can be implemented in a high level procedural orobject-oriented programming language to operate in conjunction with acomputer system. However, the programs can be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language.

[0066] Each such computer program can be stored on a storage medium ordevice (e.g., CD-ROM, hard disk or magnetic diskette) that is readableby a general or special purpose programmable computer for configuringand operating the computer when the storage medium or device is read bythe computer to perform the procedures described. The system also may beimplemented as a computer-readable storage medium, configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner.

[0067] Further, while the invention has been shown and described withreference to an embodiment thereof, those skilled in the art willunderstand that the above and other changes in form and detail may bemade without departing from the spirit and scope of the followingclaims.

What is claimed is:
 1. A method for fitting a set of upper and lower teeth in a masticatory system of a patient, comprising: modeling a set of teeth in a predetermined position; and generating a plurality of one or more appliances having cavities, said appliances having cavities and wherein the cavities of successive ones of the plurality appliances have different geometries shaped to receive and resiliently reposition teeth from one arrangement to a successive arrangement.
 2. A method for fitting a set of upper and lower teeth in a masticatory system of a patient, comprising: modeling a set of teeth in three or more predetermined positions; and generating an appliance having cavities for each of the three or more predetermined positions, said appliance having cavities and wherein the cavities of successive ones of the plurality appliances have different geometries shaped to receive and resiliently reposition teeth from one arrangement to a successive arrangement.
 3. A method for fitting a set of upper and lower teeth in a masticatory system of a patient, comprising: modeling a set of teeth using three or more predetermined molds or casts; and generating an appliance having cavities for each of the three or more molds or casts, said appliance having cavities and wherein the cavities of successive ones of the plurality appliances have different geometries shaped to receive and resiliently reposition teeth from one arrangement to a successive arrangement.
 4. The method of any of claims 1-3, wherein the modeling the set of teeth comprises selecting one or more arch forms specifying the ideal set of teeth.
 5. The method of claim 4, wherein the masticatory system includes jaws and wherein generating includes: registering a model of the upper and lower teeth with a model of the masticatory system; simulating the motion of the jaws to generate contact data between the upper and lower teeth; and placing a tooth in a final position based on the contact data.
 6. The method of claim 5, wherein the model is registered using X-ray data.
 7. The method of claim 5, wherein the model is registered using computed tomography data.
 8. The method of claim 5, wherein the model is registered using data associated with a mechanical model.
 9. The method of claim 5, wherein the simulating step further comprises applying kinematics to the model of the teeth.
 10. The method of claim 5, wherein the simulating step further comprises applying a constrained motion to the model of the tooth.
 11. The method of claim 5, wherein the placing step is based on a measure of undesirability to the contacts.
 12. The method of claim 11, further comprising optimizing the position of the tooth according to the measure of undesirability.
 13. The method of claim 12, further comprising minimizing the measure of undesirability.
 14. The method of claim 13, wherein the measure of undesirability is a function of one or more of Peer Assessment Rating (PAR) metrics, distance-based metrics and shape-based metrics.
 15. The method of claim 5, wherein the simulating step includes providing a library of motions.
 16. The method of claim 15, wherein the library of motions includes a protrusive motion.
 17. The method of claim 15, wherein the library of motions includes a lateral motion.
 18. The method of claim 15, wherein the library of motions includes tooth-guided motions.
 19. The method of claim 5, wherein the simulating step includes applying physical forces to one jaw.
 20. The method of claim 5, wherein the placing step further includes updating the computer representation of the masticatory system with new patient data.
 21. The method of claim 20, wherein the patient has a first teeth model, further comprising: scanning the teeth of the patient to generate a second teeth model; matching the second teeth model with the first teeth model; applying a final position transform to the second teeth model; and adjusting the position of teeth in the second model based on new information.
 22. The method of claim 21, wherein the matching step compares correspondences between the first and second teeth models.
 23. The method of claim 22, wherein the correspondences include feature correspondences.
 24. The method of claim 21, wherein the new information includes information from a new prescription. 